How to Determine Water Pressure by Height of Tower

Written by paul dohrman

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Water runs downhill. This is the basis for how the height of water towers provides pressure to your tap water. In ancient times, this was the basis for how fountains worked without motors. Each foot of height of a water tower provides 0.195 Kilogram per square inch (PSI).

Skill level:

Easy

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Instructions

1

Imagine a column demarcation inside the water tower that has a cross section of one foot by one foot, and a height equal to the height of the tower. The weight of the water outside of this demarcation doesn't contribute to the net upward or downward pressure on the water in the column. Therefore, the water inside the demarcation can be considered in isolation.

2

Weigh the water in the column. A cubic foot of water weighs 283 Kilogram. So each foot of height adds 283 Kilogram of downward force.

3

Multiply the height in feet by 62.4 to get pounds per square foot.

4

Divide by 144 to get pounds per square inch (PSI), i.e. multiply the height by 0.43 to get the pressure in PSI. This will be the pressure that the tower exerts. If h is the height in feet, the formula is Water Pressure = 0.43h PSI.

Tips and warnings

Measuring in metric units is much easier--or at least uses rounder numbers--since water weighs 1 gram per cubic centimetre. Such units are written in Pascals (Newtons per square meter). The conversion can therefore be found out as follows: If water weighs 1g/cm^3, then it equals 100^3g/m^3 or 1,000kg/m^3. Imagine a partition one meter by one meter and of height equal to the water tower's height, h. The mass of the column is then 1,000h, if 'h' is in meters. Multiply the mass by the gravitational acceleration constant to get weight: 1,000h*9.8m/s^2 = 9800*h Newtons per square meter per meter of tower height = 9800 Pascals per meter of tower height.

For an accurate measurement of how much pressure your tap will have, you have to find not the height of the tower but the difference between the height of the tower and your tap. Another complication is that the tower is not always full. So the above actually calculates the maximum pressure possible, not necessarily the actual pressure.